Well lets see here I am a big time Back Metal/Death Metal fan so here is my list:
Burn The Priest
Corrosion of Conformity
Dismember
Children of Bodom
The Black Dahlia Murder
Canibal Corpse
Morbid angel
Grave
SEPULTURA
SOUL FLY
Down
Dimmu Borgir
Dream Theater Opeth
Life Of Agony
Zyklon
The Crown
As I lay dying
At the Gates
Pantera
Lamb Of God
Bio Hazard
Brujeria
Metallica(Old Stuff)

On another note I hate mainstream metal. It just seems nowadays that these Nu Metal Bands(Limp Bizkit,Korn,Linkin Park etc) lack total talent and that their image is everything.